Hier noch ein Screenshot, wo zu sehen ist, dass alle Unterordner der Konten fehlen.

Hallo Matthias, bitte in der nächsten Antwort den Screen shot einfügen. Sieht dein Thunderbird-Hauptfenster beim Start etwa so aus wie in meinem Bild, mit einer Aufforderung eine bestehende E-Mail-Adresse einzurichten?

Dear Sir or Madam, Suddenly, all subfolders containing all emails have disappeared from all accounts. There is also no longer a junk folder. How can I restore it? Kind regards, Matthias Brockmann

Right-click the account in the Folder Pane, Subscribe..., Refresh. Can you see the list of missing folders and subscribe them (check the boxes)?

Dear Sir or Madam, no, there is no "Subscribe…" and then "Update" option when right-clicking on any of the accounts.

This option is not available for any of my accounts. It's not available in the settings either, nor within the individual account settings. The only options are "New Folder," "Reset Folder Order," and "Mark All Folders as Read." Even though I have the latest version of Thunderbird.

Dear Sir or Madam, no, there is no "Subscribe…" and then "Update" option when right-clicking on any of the accounts.

This means that you have created POP email accounts. The "Subscribe" option only exists for IMAP accounts

In order to progress in our diagnostic search please show the screen shot which you announced or reply to my question "Sieht dein Thunderbird-Hauptfenster beim Start etwa so aus wie in meinem Bild, mit einer Aufforderung eine bestehende E-Mail-Adresse einzurichten?"